Blasting caps



May 11, 1965 A. -J. BAROCCA BLASTING GAPS Original 'Filed Feb. 8, 1960 FIG. 2

INVENTOR. ALDO JOSEPH .BAROCCA BY ATTORNEY l t I United States Patent 3,182,592 BLASTING CARS Aldo Joseph Barocca, Alton, Ill., assignor, by mesne assignments, to Commercial Solvents Corporation, a

corporation of Maryland Original application Feb. 8, 1960, Ser. No. 7,102. Divided and this application Aug. 1, 1963, Ser. No. 303,708

2 Claims. (Cl. 102-28) This invention relates to blasting caps and particularly to electric blasting caps adapted for use with liquid oxygen explosives.

Liquid oxygen explosives consist of an absorbent fuel impregnated with liquid oxygen. Such explosive charges are simple to assemble and the impregnation with liquid oxygen normally occurs at the blasting site. Thus, these materials are exceedingly safe since their components have no explosive properties until they are mixed. Because of the safety and economy normally attendant to such charges, they are commercially attractive. Such explosives are normally satisfactory and compare favorably in strength with standard commerical explosives. However, liquid oxygen explosives do have one serious disadvantage. They are more difiicult to initiate than standard commercial explosives, and in the past it has not been found practical to tire more than two such charges in series. When attempts have been made to include a larger number of liquid oxygen explosive charges in series firing, they have been unsuccessful. It is believed that this difliculty is due primarily to the desensitization of the explosive charges in the detonator. when subjected to liquid oxygen at its boiling point (182 C.). Because of this, standard commercial electric blasting caps cannot normally be relied upon for the initiation of liquid oxygen explosive charges in series firing.

It is, therefore, an object of the present invention to provide a new and novel electric blasting cap that can be utilized for series firing of liquid oxygen explosive charges. A further object of this invention is to provide an electric blasting cap that will operate reliably in conjunction with liquid oxygen explosives. A more specific object is to provide an electric detonator containing explosive charges that are not desensitized at the low temperatures attendant to liquid oxygen explosive charges.

In accordance with this invention, these and other objects are accomplished, generally speaking, by providing a normal lead styphnate-graphite electric detonator ignition mixture for use in conjunction with liquid oxygen explosive charges. More specifically, this invention contemplates an electric detonator having a loose ignition charge of from about 95% to about 99% normal lead styphnate mixed with from about 5% to about 1% graphite, a bridge wire embedded in the ignition mix, an initiator having a strength at least equivalent to that of lead azide, and a base charge having a strength at least equivalent to pentaerythritoltetranitrate or cyclonite. Generally it is preferred to utilize lead azide as the initiator and cyclonite or pentaerythritoltetnanitrate as the base charge. When explosive materials having lesser strengths are present, considerable difiiculty is encountered in detonating the liquid oxygen explosives and, at best, only low order detonations are obtained.

As indicated above, the loose ignition charge of the present invention can contain between about 95% and about 99% normal lead styphna-te and the balance graphite. When less than about 1% graphite is employed, the functioning of the detonator at low temperatures is seriously impaired and ignition becomes unreliable. On the other hand, when the amount of graphite in the ignition mixture exceeds about 5%, it results only in dilution of the igniter and in diminution of its effectiveness in activating the initiator. In most instances, it is preferred to use an ignition mixture containing about 98% normal lead styphnate and about 2% graphite. However, it will be readily appreciated that the composition can be varied "within the range indicated.

plishes its objects will be more readily understood by reference to the following specific embodiment thereof and drawing wherein FIGURE 1 is a longitudinal section of the complete detonator, and

FIGURE 2 is a schematic showing of one method for using the detonator of FIGURE 1. t

In the specific embodiment and throughout the specification, all proportions are expressed in parts by Weight.

Referring to FIGURE 1, a detonator in accordance with the present invention was prepared by charging a base charge 3, i.e. about 6.1 grains of cyclonite, into gilding metal case 1 to a density of about 1.4- grarns per cc. About 3.8 grains of lead azide initiator 4 were positioned above the base charge 3. About 1.1 grains of a loose ignition mixture 5 consisting essentially of 98% normal lead styphnate and 2% graphite was then positioned above the lead azide initiator 4-. A sulfur bridge plug 7 carrying a pair. of leadwires 8 with a bridge wire 9 extending between the ends thereof was then placed in the detonator case 1 above the ignition mixture 5, the lead wires 8 extending into the loose ignition mixture 5 so that the bridge wire 9 was embedded in and completely surrounded by the lead styphnate-graphite mixture. The detonator case 1 was sealed by a layer of pitch above the sulfur bridge plug '7, and a layer of sulfur above the pitch served to lock the waterproofing pitch in position.

To illustrate the effectiveness of the instant detonator six 40 pound charges of a liquid oxygen explosive C1, C2, C3, C4, C5 and C6 were positioned Wllhll'l separate bore holes in a Work face ll), as illustrated in FIGURE 2 and spaced for effective series firing. Blasing caps B1, B2, B3, B4, B5 and B6 made in accordance with the procedure described above Were inserted, respectively,

into each of these charges and connected in series by electric lines to a blasting machine 12 capable of providing a firing current of at least one ampere to each of the detonators of the assembly. When the current was applied to this circuit, each of the six liquid oxygen explosive charges detonated, completely shattering the surrounding work face. The number of explosive charges thus fired in series can be increased as desired. It is only limited by practical considerations such as a readily available source of electrical energy and the number of explosive charges that can be conveniently prepared for concurrent firing.

Detonators difi'ering from those described above only in the composition of the ignition mixture are, at best, only partially satisfactory in liquid oxygen explosive operations. For example, such detonators having an ignition composition of mercury fulminate and ground cannon powder as set forth in US. 2,825,639 to Thomas I. Mulqueeny et al., are completely inoperative for firing liquid oxygen explosives. In fact, using detonators having such an ignition charge liquid oxygen explosives cannot even be detonated individually. When normal lead styphnate alone is used as the igniter, the results are not reliable in series firing and not more than two such explosive charges can be fired in series with complete predictability. Similar undesirable results are obtained when using other standard ignition compositions.

' This application is a division of U.S. patent application Serial No. 7,102 filed February 8, 1960, now abandoned.

Although the invention has been described in considerable detail in the foregoing, it is to be understood that the purposeof such detail is only for clarification of the invention and that many modifications can be made by f those skilled in the art without departing from the spirit I and scope of the invention except as it is limited by the appended claims. 1

A and a base charge selected from the group consisting of cyclonite and 'pentaerythritoltetranitrate.

2. A blasting assembly comprising a plurality of liquid oxygen explosive charges adapted to be fired in series,

an electric detonator. in association with each explosive charge and connected in series to a common source of electrical energy, each of the electric detonators having an ignition mixture of from about 95% to about 99% normal lead styphnate and from about 5% tetranitrate.

v 7 References Cited by the Examiner UNITED STATES PATENTS 2,682,221 6/54 Sauvage' 2 too- 28 2,696,191 12/54 Sheehan i 102- 28 X 2,767,655 10/56 Seavey '102--28 2,987,997

SAMUEL FEINBERG, Primary Examiner,

to about 71% graphite, a lead azide initiator and a base charge selected from the group consistinglof cycloniteand pentaerytluitol- V 6/61 Ireland '102 2s 

1. A BLASTING ASSEMBLY COMPRISING A LIQUID OXYGEN EXPLOSIVE CHARGE AND AN ELECTRIC DETONATOR FOR SAID CHARGE, SAID DETONATOR HAVING AN IGNITION MIXTURE OF FROM ABOUT 95% TO ABOUT 99% NORMAL LEAD STYPHNATE AND FROM ABOUT 5% TO ABOUT 1% GRAPHITE, A LEAD AZIDE INITIATOR AND A BASE CHARGE SELECTED FROM THE GROUP CONSISTING OF CYCLONITE AND PENTAERYTHRITOLTETRANITRATE. 